HI , I've had a battle with my 2001 blazer 4wd 4.3 85kmiles. Started with a p0335 code only...shimmed out ckp sensor and code and symptoms are gone. Now and almost instantly , the mil light is on and flashing. Code p0300 is now set. After a set of plugs and a cap it still shows same cylinders miss-firing; #1 and #4. #4 miss-firing 5 times more...heres the odd thing at exactly 2k rpm it is fine no miss-fire , anything above or below the missfires start. Also dont know if it is relative wont ckp-relearn...it now goes into wot 6k rpm, but no cut out (afraid to over rev.)Please help ....I've borrowed a recently refubished and updated MODIS....

 

Are you getting consistent readings from the CKP sensor?

 

sorry dont know how to access ckp readings on this modis,the only thing fluctuating is 02 values from 87mv to near 800mv

 

p0300 still there,this is whats been done;new cap and rotor (two different makes)wires,ckp,cam sensor,tps,distributor,coil,ign.module,fuel pump x2, plugs.Engine spark knocks and scanner shows no ignition retarding at any engine speed ,stays at 0.Idle seems low at 620 rpm .Countless missfires on #1 and #4 this has never changed.While pumping the throttle there are no missfires and will not go into ckp calibration tried techII and modis no result

 

I had your same problem and pretty much changed everything you did and found out after I changed the cap and rotor again Pull up on your rotor while it is still connected and see if there is movement while you have the rotor pulled up if you do you have a bad distributor I changed mine and still running fine

 

im haven kind of the same issue it misfires when its cold but after it warms up and i restart it it runs just fine idk whats going on with it but its makin me crazy

 

P0335 is a problem in the CKP signal wire, (Brown with white stripe wire) between the CKP sensor and the PCM. When you moved the CKP you probably disturbed the wire, might be a loose connection close by. Whenever the CKP is moved, the CKP relearn MUST be done, (coolant must be above 150F before initiating the relearn.) If the PCM will not complete the relearn, try it 3 times, if it still will not relearn, check the tone ring for damage, make sure the CKP sensor is aligned properly in the bracket, check for proper routing of the signal wire to the PCM, and make sure the distributor is timed correctly.

After moving the CKP sensor: If the relearn is not completed, the PCM is still using the data from where the CKP sensor used to be, which is now incorrect, which means cam retard is also incorrect. Bottom line, it means the ignition timing is incorrect and the PCM has no idea where timing is, or where it's supposed to be, and the engine will probably misfire and run like poop. Ain't no 2 ways about it, ya gotta get it to relearn.